I think the easiest method is rendering a CGI floor. You'll get the correct perspective. I've used basic 3D programs like Bryce & basic 3ds max to render some floors. But for the most part, I'm forever shooting my own library of floors. Especially large tarmac textures. Sometimes I have to stitch it all together which can be a pain.

Bryce? I never thought about it... now to see if I can find the old old copy i used to have...

The older versions were still pretty shitty. The rendering engine never gave you anything really worthwhile (realistic looking). The newest versions are getting much better. But you still need to apply a photo texture to a 3d object to achieve the best looking output.